That is the voltage of a battery at rest and fully charged. If truck is running and that's all there is, Bad ground to alt, loose belt, bad alt....and the light on when running supports that. Take alt to O'Reilly's, Autozone or equivalent to get tested for free. That is your next step. Thanks for the update Mike.
I realize you are pretty rural. Hope there is some place closer than Concordia to test. It's good to go to a testing place that you are sure has the alternator in stock, so you only make one trip. If you are sure it's all good and grounded and spinning, it is probably bad, but I, myself, don't trust myself, so I need someone that tests it outside of truck, away from any mistakes or bad issues. But I don't live 15 miles from O'Reillys either. Maybe just try it with a one wire setup. Batt hot to alt hot. Heavy gauge wire (10 or 8 ga)
